In recent years, printing plates made of a resin have often been used in the printing field. Particularly, flexographic printing, which is characterized by using flexible printing plates and is increasingly important among various printing techniques, mainly employs printing plates made of the resin.
In printing inks, various organic solvents are used according to applications. When printing plates are made of the resin, they often have insufficient resistance to organic solvents and present problems such as insufficient printing precision and insufficient durability of the printing plates themselves. Therefore, printing plates or blank printing plates made of the resin are demanded to have excellent resistance to various solvents.
Meanwhile, it has been already known that a polymer produced from polycarbonate diol is applicable to a photosensitive resin composition for production of a blank printing plate. For example, Patent Document 1 discloses a resin composition for a laser-engravable blank printing plate and a blank printing plate comprising a resin produced from polycarbonate diol and inorganic fine particles.
Patent Document 2 discloses polycarbonate diol comprising a repeating unit which corresponds to the formula (2) of the present application wherein R2 is a hydrocarbon group having 2 to 14 carbon atoms.
Patent Document 3 discloses polycarbonate having an ether structure having 3 to 20 carbon atoms.
Patent Document 4 discloses polyether polycarbonate diol comprising a polyoxytetramethylene glycol unit as a component.
Patent Document 5 discloses polycarbonate comprising aliphatic diol and/or polyether diol having 3 to 200 carbon atoms.
Patent Document 6 discloses a technique wherein a polymer comprising polycarbonate diol is used as a photosensitive layer of a planographic blank printing plate.
Patent Document 7 discloses a technique wherein urethane-modified polycarbonate containing an oxyethylene group as a repeating unit is used as a water-soluble photosensitive resin composition for a printing plate.
[Regarding Method for Producing Conductive Layer]
A radio-frequency identification (RFID) tag is used for tracking inventories or confirming the validity of commodities and also used for the purpose of tracking and authenticating other products. The RFID tag needs an antenna for transmitting/receiving data by radio waves. This antenna is formed by an approach such as a method for embedding an embeddable winding, a printing method using a conductive ink, a method for etching a conductive thin film, and a plating technique.
The RFID tag formed by the printing method requires lower cost than that of its counterparts for production. Furthermore, it can provide a visually beautiful aspect. This is particularly important for taking into consideration the use of an antenna printed in ink for tracking retail goods. This is because general retail goods trackers employ large obtrusive tags, compared to more decorative tags produced by using the antenna printed in ink.
Patent Document 8 describes a method for producing an RFID tag using a screen method.
Moreover, in electromagnetic shielding applications, for example, Patent Document 9 discloses an electromagnetic shielding member which is formed by printing an electromagnetic shielding pattern onto a transparent substrate by a gravure printing or gravure offset printing method using a conductive ink containing silver particles.
[Regarding Method for Producing Organic Light-Emitting Layer]
An organic electroluminescence (hereinafter, abbreviated to “organic EL”) element comprises an organic light-emitting layer made of an organic light-emitting material formed between two electrodes facing each other and emits light when electric current is applied to the organic light-emitting layer. The film thickness of the light-emitting layer is important for efficiently emitting light and must be as thin as approximately 100 nm. Furthermore, display production using this element requires highly defined patterning.
The organic light-emitting materials are classified into low-molecular-weight materials and high-molecular-weight (or polymer) materials. The low-molecular-weight materials are generally made into a thin film by a resistance heating deposition method or the like, and this film is patterned via a fine pattern mask. This method has the problem that the use of a larger substrate offers lower patterning precision.
Thus, a currently attempted method employs the high-molecular-weight (or polymer) material as an organic light-emitting material and comprises dissolving the organic light-emitting material in a solvent to prepare a coating solution, which is in turn used to form a thin film by a wet coating method. The wet coating method for thin film formation includes spin coating, bar coating, discharge coating, and dip coating methods. These wet coating methods have difficulty in highly defined pattering and color-coding with three colors RGB. A printing method which excels at color-coding and patterning is probably most effective for thin film formation.
However, a method using a hard printing plate made of metal, such as a gravure printing method, is unsuitable for a glass or resin substrate serving as an organic EL display substrate, since the hard printing plate causes large damage to the substrate. Thus, an offset printing method using an elastic rubber blanket or a letterpress printing method (flexographic printing method) also using an elastic rubber plate or photosensitive resin plate is preferable. Actually, as attempts using these printing methods, Patent Document 10 proposes a method based on offset printing, and Patent Document 11 proposes a method based on letterpress printing.
On the other hand, the high-molecular-weight (or polymer) organic light-emitting materials are poorly soluble in water and alcoholic solvents and must be dissolved or dispersed in organic solvents for preparing a coating solution. Among them, aromatic organic solvents such as toluene and xylene are preferable. Therefore, an aromatic organic solvent-containing ink is often used as an ink made of an organic light-emitting material (hereinafter, referred to as an “organic light-emitting ink”).
However, a rubber blanket used in offset printing has the problem that it easily swells or deforms due to aromatic organic solvents such as toluene and xylene. Offset printing is a printing technique comprising: applying a coating solution to a patterned plate; transferring the coating solution to an elastic blanket; and further transferring the coating solution from the blanket to a substrate to be printed. The blanket that mediates the transfer of the coating solution must have elasticity, and blankets made of a rubber are generally used. The types of rubbers used are diversified from olefin-based rubbers to silicone-based rubbers. All of these rubbers easily swell or deform due to aromatic organic solvents such as toluene and xylene. Plates made of a rubber, photosensitive resin, or the like used in flexographic printing also generally had the problem of poor resistance to organic solvents.
Patent Document 12 discloses that in a letterpress printing method, the use of a water-developable letterpress plate comprising a photosensitive resin produces a plate that is highly resistant to organic solvents and less prone to mass change or deformation even using organic light-emitting inks, since the polyamide-based photosensitive resin is made of a material rich in a hydrophilic resin.
In recent years, a so-called flexo CTP (computer to plate) technique has been developed which comprises: placing a thin light-absorbing layer called a black layer onto the surface of a photosensitive resin; directly forming a mask pattern on the photosensitive resin plate by laser light irradiation; then causing crosslinking reaction by light irradiation via the mask; and then washing off the unexposed (uncrosslinked) portion by use of a developing solution. This technique has been increasingly adopted in terms of the effect of improving the efficiency of printing plate making.
Alternatively, examples of a method that eliminates the need of development may include a method for directly laser-engraving a blank printing plate. The preparation of letterpress printing plates or stamps by this method has already been performed, and materials used therein have also been known. By way of an example, Patent Document 13 describes a method for extruding a heat-melted photosensitive resin onto a cylindrical support using an extrusion molding apparatus and then forming a photosensitive member using a calendering apparatus.
[Regarding Method for Producing Liquid Crystal Orientation Film]
The utilization of liquid crystal materials as devices generally requires allowing liquid crystal to align in a fixed sequence (orientation). This molecular orientation is changed depending on the influence of an external field such as an electric field, magnetic field, shear force, or interface. By using optical properties changed thereby, liquid crystal is utilized in various electronic fields.
The orientational control of liquid crystal is generally achieved by forming an orientation film on substrate surface with which the liquid crystal comes into contact. The orientation film are broadly classified into homeotropic alignment membranes in which liquid crystal is oriented in a homeotropic direction or a direction slightly tilted from the homeotropic direction, relative to a substrate, and into homogeneous alignment membranes in which liquid crystal is oriented in a homogenous direction or a direction slightly tilted from the homogenous direction, relative to a substrate. These membranes are properly used according to display modes. Of them, homogeneous alignment membranes used in twisted nematic (TN) or super twisted nematic (STN) modes conventionally widely used are particularly important from an industrial standpoint. Polyimide membranes that have undergone a rubbing process are excellent in uniform orientation or reliability and are widely used as the homogenous alignment membranes.
A method for printing a liquid crystal orientation film often uses a glass substrate as a substrate. Therefore, a method using a hard printing plate made of metal, such as a gravure printing method, is unsuitable. A letterpress printing method (flexographic printing method) using an elastic rubber plate or photosensitive resin plate is proper and is therefore generally used.
Actually, offset printing methods for this purpose are described in, for example, Patent Documents 14 and 15. Moreover, Patent Document 16 describes a method for producing a resin letterpress plate having a relatively large dimension in response to market demands involved in the upsizing of liquid crystal displays.
Plates used in letterpress printing generally used or offset printing are prepared by the following method: a negative film is placed on the surface of a photosensitive resin applied to a substrate; and the photosensitive resin is irradiated through the negative film with light rays such as UV rays. By this method, the photosensitive resin is cured in a site where light rays pass through the negative film, whereas the photosensitive resin is uncured in a site where light rays are blocked by the negative film. Thus, after irradiation with light rays, the uncured photosensitive resin is washed off by development to obtain a resin letterpress plate having a relief composed of the site containing the cured photosensitive resin.
In recent years, a so-called flexo CTP (computer to plate) technique has been developed which comprises: placing a thin light-absorbing layer called a black layer onto the surface of a photosensitive resin; directly forming a mask pattern on the photosensitive resin plate by laser light irradiation; then causing crosslinking reaction by light irradiation via the mask; and then washing off the unexposed (uncrosslinked) portion by use of a developing solution. This technique has been increasingly adopted in terms of the effect of improving the efficiency of printing plate making.
[Regarding Method for Producing Black Matrix]
A resin black matrix comprising a light-shielding material, a resin, and a solvent has been used as a black matrix for a liquid crystal display color filter. A composition comprising a resin and a light-shielding material is dispersed in an appropriate solvent to prepare a paint, which is then applied to a liquid crystal substrate and patterned to form a resin black matrix.
Patent Document 17 discloses a resin black matrix which comprises a light-shielding material and a resin and which is additionally supplemented with pigments of blue color, purple color, and the like as complementary colors.
Patent Document 18 proposes a resin black matrix comprising: an organic pigment system comprising an organic black pigment and/or a pseudo-black mixed organic pigment which is obtained by mixing at least two or more organic pigments of colors selected from red, blue, green, purple, yellow, cyanine, and magenta; at least one or more light-shielding materials selected from carbon black, chromium oxide, iron oxide, titanium black, and aniline black; and a photosensitive resin.
Moreover, Patent Document 19 proposes a material for forming a black matrix, comprising a photopolymerizable compound, a photopolymerization initiator, an alkali-soluble resin, and a black pigment characterized by being a mixture of at least two members including resin-coated carbon black and metal oxide.
Furthermore, Patent Document 20 describes a resin black matrix comprising a titanium oxynitride and a resin.
Furthermore, Patent Document 21 discloses a resin black matrix comprising insulating film-surface-coated titanium oxynitride particles and a resin.
Furthermore, Patent Document 22 describes a resin black matrix comprising a polyimide or acrylic resin as a resin and carbon black and titanium oxynitride as light-shielding materials.
[Regarding Method for Producing Colored Layer for Color Filter]
In recent years, demands have been ever increasing, such as higher definition, weight reduction, and lower cost of input/output elements such as color filter imaging elements or color image displays. In response to the demands, the development of various elemental technologies essential to these apparatuses is proceeding. Particularly, for image displays, basic techniques are changing. Liquid crystal displays, which are light in weight, space-saving, and portable, have been prevailed rapidly instead of conventionally dominating CTR.
Although the liquid crystal displays are getting easier to use, displays having a large area are still not sufficiently low in cost. Thus, various methods have been attempted to reduce cost. Examples of such methods may include: modification from an active matrix liquid crystal mode having individual TFT pixels to a ferroelectric liquid crystal mode in which the liquid crystal itself has switching properties; and improvement of a simple matrix mode typified by STN liquid crystal.
A color filter indispensable to color image display partly occupies the large proportion of cost required for liquid crystal displays. This color filter generally comprises a large number of fine pixels dividing a full screen, each of which has three sub-pixels each comprising a fine optical filter element (approximately 100 μm or smaller) that passes red (R), green (G), or blue (B) light therethrough. A method has been prevailed which comprises providing an opaque grid-pattern mask (black matrix), each zone of which surrounds each fine filter element such that a black color is distinctively defined or the color mixture between adjacent colors is prevented to improve color reproducibility. Thus, the color filter has a complicated and fine structure and therefore posed a challenge to the production with high precision and at low cost.
A conventionally known method for producing a color filter is a so-called staining method which involves repeating, for three colors, red, green, and blue, the steps of: placing, on a substrate, a mordant layer comprising a hydrophilic polymer such as gelatin, casein, glue, or polyvinyl alcohol; and staining the mordant layer with a dye to form a colored layer. This method relatively easily responds to spectral characteristics required for filters, by virtue of many available dyes. The step of staining the mordant layer adopts a difficultly controllable wet step of dipping the mordant layer in a staining bath containing the dye dissolved therein. Moreover, this method requires forming an intermediate layer for resist printing after the formation of the colored layer made of each color and has a complicated photolithography step for each color in the patterning of the mordant layer or for resist printing. Therefore, the method disadvantageously has a long takt time and poor yields. Moreover, the dye used in the staining has low heat resistance and light resistance. Therefore, the resulting color filter had a durability problem.
On the other hand, methods disclosed in, for example, Patent Documents 23 to 26 are so-called pigment dispersion methods wherein a colored resin membrane comprising a photosensitive resin mixed with a coloring material such as a pigment is used as a color filter layer. These methods eliminate the need of the staining step after color filter layer formation, since the colored resin comprises the coloring material such as a pigment from the first. Thus, the formation of an intermediate layer for resist printing is also unnecessary. Therefore, the methods have a simpler step than that of the staining method.
Moreover, a printing method forms fine pixels by a highly precise printing technique such as planographic offset printing or screen printing. For example, Patent Document 27 proposes a color filter characterized by comprising: a light-shielding membrane having a large number of openings formed at positions to be provided with pixel portions; and the same number of colored layers as the number of a plurality of different colors of the pixel portions, the colored layers being formed with a material transparent to visible light and each having colored portions of the same color at positions corresponding to the openings of the light-shielding membrane, wherein the colored layers are stacked such that the colored portions of the same color do not overlap with the other colored portions of colors different therefrom, and wherein the colored portions form, through the openings of the light-shielding membrane, the alignment of pixel portions of a plurality of different colors.
Furthermore, Patent Document 28 proposes a method comprising: applying, to preformed openings of a black matrix, a coloring paste prepared by adding a heat-resistant pigment to a polyimide precursor; and after pattern formation, curing the polyimide precursor by heating to form a colored layer of each color of red (R), green (G), and blue (B).
[Regarding Method for Producing Photoelectric Conversion Layer for Organic Thin-Film Solar Cells]
Inorganic thin-film solar cells comprising an Si, GaAs, or CuInGaSe thin film or the like have been developed as thin-film solar cells. However, their production requires an expensive semiconductor production facility, resulting in high production cost. Thus, these solar cells had the problem that they have difficulty in achieving electric generation cost equal to or lower than general electricity expense in terms of total cost.
Thus, to solve the problem, the development of organic thin-film solar cells which do not require an expensive semiconductor production facility and can achieve low production cost has been actively proceeding in recent years.
The general structures of such organic thin-film solar cells are disclosed in Non-Patent Documents 1 and 2.
The organic thin-film solar cell is a solar cell comprising an organic thin-film photoelectric conversion layer disposed between two dissimilar electrodes, wherein the photoelectric conversion layer has electron-donating and electron-accepting functions. The organic thin-film solar cell may be produced in a simper step than that of inorganic thin-film solar cell production using an Si, GaAs, or CuInGaSe thin film or the like and may be adaptable to a larger area at low cost.
Patent Document 29 discloses a photoelectric conversion element having a simple structure and high photoelectric conversion efficiency. A method for producing a photoelectric conversion layer used therein is a spin coating method.
Patent Document 30 discloses methods such as die coating, roll coating, and spray coating as methods for producing a photoelectric conversion layer.
[Regarding Method for Producing Patterned Thin-Film Semiconductor Layer]
In recent years, electronic paper, RFID tags, and so on have received attention. They need a semiconductor. However, current transistor production processes require a vacuum process and a photo process, resulting in high production cost. Therefore, the realization thereof requires more inexpensive and larger-scale production than that of conventional transistors. Moreover, it is also desired that a transistor should be formed on a flexible substrate.
Therefore, transistors, particularly, organic transistors, produced using a printing method have received attention (Patent Document 31).
In organic transistor production, a resin film can be used as a substrate to be printed, since a semiconductor can be processed at a low temperature. Moreover, the semiconductor is made of organic matter. Therefore, a solution containing this organic matter dissolved in a solvent may be processed in the same way as in a printing ink by a printing method.
[Regarding Method for Producing Photosensitive Layer of Electrophotographic Photoreceptor]
Electrophotography used in a copier, printer, or the like comprises: electrically charging the whole surface of a photosensitive layer on a photoreceptor drum; then forming a latent charge image of a document or the like in a latent image-forming portion; subsequently developing this latent image into a visible image in a development portion by use of charged toner; then transferring the image to a recording medium such as plain paper in a transfer portion; and thermally fixing the image thereon in a fuser portion to obtain a hard copy. In this technique, the photoreceptor is usually grounded via a conductive layer for improving the amount of an electric charge in charging, providing a light attenuation effect in light exposure, and using it as a bias electrode in development.
Conventionally, photosensitive materials comprising inorganic photoconductive substances such as selenium, selenium-tellurium alloys, cadmium sulfide, and zinc oxide have been used widely in a photosensitive layer of an electrophotographic photoreceptor. In recent years, the study of organic photoconductive substances has been proceeding which are easily synthesized and are characterized in that, for example, they exhibit photoconductivity in an appropriate wavelength region.
For example, Patent Document 32 discloses an electrophotographic photoreceptor which is obtained by: applying a coating solution for a charge generation layer by dipping onto an aluminum drum used as a photoreceptor drum; then applying a coating solution for a charge transport layer thereonto by dipping; and further providing a protective layer for the photosensitive layer as means for improving durability.
Moreover, Patent Document 33 discloses an electrophotographic photoreceptor comprising a flexible nonmetallic conductive support and a photosensitive layer formed on the conductive support, wherein the photosensitive layer comprises a plurality of thin films including a charge generation layer. A thin film formation method disclosed therein includes application methods such as deposition, codeposition, spray coating, blade coating, casting, spinner coating, bead coating, wire bar coating, roller coating, and curtain coating methods.
Furthermore, Patent Document 34 also discloses thin film formation methods using a photoconductive composition in an electrophotographic photoreceptor or the like, including application methods such as spin coating, casting, dipping, bar coating, and roll coating methods.
[Regarding Method for Producing Electron-Accepting and/or Electron-Donating Organic Layers Constituting Photovoltaic Element for Photosensor]
Conventionally, monocrystalline, Polycrystalline, or amorphous Si has been used in the production of photovoltaic elements. The development of photovoltaic elements using organic materials has been proceeding for developing inexpensive and low toxic photovoltaic elements.
Photovoltaic elements that utilize an internal electric field generated by a Schottky junction, MIS junction, or p-n heterojunction based on an n-type inorganic semiconductor/p-type organic semiconductor junction are known as the photovoltaic elements produced using organic materials. The photovoltaic element is desired to have high energy conversion efficiency, since it is an element that converts light energy to electric energy (voltage×electric current). The photovoltaic elements based on the junctions could not be expected to have high conversion efficiency.
To solve such problems of the photovoltaic elements, a photovoltaic element has been developed using an organic/organic p-n heterojunction (Non-Patent Document 3). This photovoltaic element utilizes an electric field generated by a junction between an electron-accepting organic layer and an electron-donating organic layer. Light irradiation through a transparent electrode and photocharge generation caused by two organic materials can be achieved. Therefore, this photovoltaic element has been known to have an advantage such as wider spectral sensitivity than that of the photovoltaic elements described above.
A method using a vacuum deposition process (Patent Documents 35 and 36) and a spin coating method as a wet film formation method (Patent Document 36) have been used as methods for producing the electron-accepting and electron-donating organic layers constituting the photovoltaic element that utilizes an organic/organic p-n heterojunction.
[Regarding Method for Producing Polysilane Thin Film of Optical Switching Element]
Conventionally, optical switching elements have been produced by an LB method. However, the optical switching element production by an LB method requires a very long time and has difficulty in achieving high degree of integration of an element having a fine pattern. Therefore, this approach has been known to present a problem in terms of the practical production of elements.
Thus, to solve the problem, Patent Document 37 discloses an optical switching element which comprises an optical switching portion selectively formed on a portion of a polysilane thin film formed on a substrate and which is made of polysiloxane and photochromic materials, wherein the optical switching element is produced in a simpler step and operated using a usual light source. In this context, a process for producing the polysilane thin film disclosed therein adopts a spin coating method.
[Regarding Processes for Producing Bank, Etc.]
Organic EL displays have been expected as display devices in place of liquid crystal displays, along with higher-quality pictures and lower power consumption of cellular phones, personal digital assistants, or the like. An organic EL element used as a display element in this organic EL display has a structure comprising a lower electrode (also referred to as a pixel electrode), an organic EL layer, and an upper electrode sequentially stacked on a substrate made of glass or the like and emits light when electric current is applied to between the upper and lower electrodes. The organic EL layer may have, for example, a structure consisting of a light-emitting layer or may have, for example, a structure comprising a light-emitting layer in combination with one or both of hole transport and electron transport layers.
When low-molecular-weight materials are used, a vacuum deposition method or the like is known as a method for forming a light-emitting layer and a hole transport layer on the substrate contained in the organic EL element. When high-molecular-weight (or polymer) materials are used, methods are known, such as spin coating, dipping, roll coating, doctor blade, and various printing methods.
In recent years, an inkjet method has received attention which has the advantage that it can efficiently form an organic EL layer for each organic EL element portion forming a pixel (hereinafter, abbreviated to a “pixel-forming portion”) and easily achieves arrangement (color coding) of each organic material to emit light of each color of RGB (Patent Document 38). In this context, when this inkjet method is used, a liquid substance containing the organic material as an ink discharged from the nozzle of an inkjet head may be leaked from a target pixel-forming portion to be landed on to a pixel-forming portion adjacent thereto. Such leakage is caused because a gap (spacing) for forming drops is formed to some extent between the inkjet head and the substrate. Specifically, when an ink is discharged from the nozzle of the inkjet head, the ink is discharged in varying directions (angles) due to soil or the like attached to the tip of the nozzle or exhibits stray fly due to influence such as air flow. As a result, a position on which ink drops are landed through the gap may deviate from the desired target position.
Moreover, in organic EL element preparation, the element is placed on a movable X-Y table, and substrate position is mechanically controlled by driving this X-Y table in most cases. Therefore, the leakage may occur due to mechanical alignment errors. In general, landing position precision determined depending on the discharge precision of the inkjet head and the alignment precision of the table is a value on the order of ±15 to 30 μm. Due to this deviation of landing position, the organic EL element is difficult to precisely form at a desired position, when the inkjet method is used without particular constitution that prevents the leakage.
Thus, a method has been proposed which comprises surrounding each pixel-forming portion by water-repellent/oil-repellent (hereinafter, abbreviated to “liquid-repellent”) banks in the organic EL element preparation (Patent Document 39). This method is a method comprising: forming a predetermined pattern onto electrodes formed on a transparent substrate to form a plurality of pixel electrodes; then forming banks which function as barriers between the formed pixel electrodes adjacent to each other; further forming a liquid-phase organic EL layer (e.g., charge injection/transport layer and/or light-emitting layer) in a region surrounded by the banks; and further forming an upper electrode thereon.
In this context, the thickness of the bank is generally approximately 1 to 3 μm. Moreover, an organic resin material such as a polyimide-based resin, polymethacrylate, or novolac-based resin is usually used as a material for the bank. Photosensitivity is often imparted to this material for facilitating patterning. Moreover, the bank surface must have low surface free energy relative to inks for imparting liquid repellency thereto. For imparting such liquid repellency to the bank surface, methods have been adopted, for example: a method comprising allowing an organic resin as a bank material to contain in advance a fluorine-containing functional group or silicon-containing additive; and a method comprising using fluorine-based gas typified by carbon tetrafluoride after patterning to plasma-treat the bank surface.
Moreover, a hydrophilic/lipophilic (hereinafter, abbreviated to “lyophilic”) property, which is opposite to the liquid repellency imparted to the bank surface, is imparted to the pixel electrode surface. ITO (indium tin oxide) for forming a transparent electrode is often used as a material for the pixel electrode. For example, organic (hydrocarbon-containing) impurities are removed by subjecting the pixel electrode surface to UV/O3 treatment or oxygen plasma treatment, which is a washing method known in the art. As a result, the lyophilicity of the pixel electrode surface can also be enhanced. For organic EL elements, the ionization potential (work function) of the ITO surface is increased by the treatment, and thus, the effect of improving hole injection efficiency can also be expected.
Thus, the liquid repellency imparted to the bank surface and the lyophilicity imparted to the pixel electrode surface can accept (compensate for) the deviation of landing position to some extent, since some ink drops, if any, landing on a portion of the bank surface are attracted by the lyophilic pixel electrode surface and uniformly patterned on the pixel electrode surface. Such an approach prevents the adjacent pixel-forming portions from being contaminated with undesired inks of the other types and therefore reduces the color mixture of inks within the pixel-forming portions, unless the inks land on the adjacent pixel electrode surfaces.
As described above, when high-molecular-weight (or polymer) materials are used, a method for producing a light-emitting layer and a hole transport layer by various printing methods is known as a method for forming a light-emitting layer and a hole transport layer on the substrate contained in the organic EL element. Patent Document 40 discloses a method based on an offset printing method. Patent Documents 41 and 42 disclose a method based on a letterpress printing method. Patent Document 42 also discloses that in a letterpress printing method, the use of a water-developable letterpress plate comprising a photosensitive resin produces a plate that is highly resistant to organic solvents and less prone to mass change or deformation even using organic light-emitting inks, since the polyamide-based photosensitive resin is made of a material rich in a hydrophilic resin.
When the organic light-emitting layer is produced by a printing method using a high-molecular-weight (or polymer) material, for example, an aromatic organic solvent such as toluene or xylene must be used as a solvent in an organic light-emitting ink containing the high-molecular-weight (or polymer) material.    Patent Document 1: Pamphlet of WO 03/022594    Patent Document 2: Japanese Patent Laid-Open No. 5-239202    Patent Document 3: Japanese Patent Laid-Open No. 2003-113237    Patent Document 4: Japanese Patent Laid-Open No. 4-214720    Patent Document 5: Japanese Patent Laid-Open No. 60-81246    Patent Document 6: Japanese Patent Laid-Open No. 2001-109139    Patent Document 7: Japanese Patent Laid-Open No. 8-328249    Patent Document 8: Japanese Patent Laid-Open No. 2003-223626    Patent Document 9: Japanese Patent Laid-Open No. 2004-277688    Patent Document 10: Japanese Patent Laid-Open No. 2001-93668    Patent Document 11: Japanese Patent Laid-Open No. 2001-155858    Patent Document 12: Japanese Patent Laid-Open No. 2006-252787    Patent Document 13: Japanese Patent Laid-Open No. 9-169060    Patent Document 14: Japanese Patent Laid-Open No. 2001-91918    Patent Document 15: Japanese Patent Laid-Open No. 6-186551    Patent Document 16: Japanese Patent No. 3221661    Patent Document 17: Japanese Patent No. 2861391    Patent Document 18: Japanese Patent No. 2552391    Patent Document 19: Japanese Patent Laid-Open No. 2000-147240    Patent Document 20: Japanese Patent Laid-Open No. 2000-143985    Patent Document 21: Japanese Patent Laid-Open No. 2001-83315    Patent Document 22: Japanese Patent Laid-Open No. 2005-75965    Patent Document 23: Japanese Patent Laid-Open No. 55-134807    Patent Document 24: Japanese Patent Laid-Open No. 60-129707    Patent Document 25: Japanese Patent Laid-Open No. 60-237441    Patent Document 26: Japanese Patent Laid-Open No. 61-105505    Patent Document 27: Japanese Patent Laid-Open No. 9-80223    Patent Document 28: Japanese Patent Laid-Open No. 2005-75965    Patent Document 29: Japanese Patent Laid-Open No 2005-116617    Patent Document 30: Japanese Patent Laid-Open No 2006-245073    Patent Document 31: Japanese Patent Laid-Open No. 2003-249656    Patent Document 32: Japanese Patent Laid-Open No. 123992    Patent Document 33: Japanese Patent Laid-Open No. 8-190209    Patent Document 34: Japanese Patent No. 3146296    Patent Document 35: Japanese Patent Laid-Open No. 5-21823    Patent Document 36: Japanese Patent Laid-Open No. 2005-93572    Patent Document 37: Japanese Patent Laid-Open No. 11-72808    Patent Document 38: Japanese Patent Laid-Open No. 10-12377    Patent Document 39: Japanese Patent Laid-Open No. 11-87062    Patent Document 40: Japanese Patent Laid-Open No. 2001-93668    Patent Document 41: Japanese Patent Laid-Open No. 2001-155858    Patent Document 42: Japanese Patent Laid-Open No. 2006-252787    Non-Patent Document 1: MATERIAL STAGE, vol. 2, No. 9, 2002, p. 37-42, J. Nakamura et al., “Organic Thin-Film Solar Cell—Utilization of Donor-Acceptor Interaction—”    Non-Patent Document 2: OYO BUTURI (a monthly publication of The Japan Society of Applied Physics), vol. 71, No. 4, 2002, p. 425-428, A. Konno “Present and Future of Organic Solar Cell”    Non-Patent Document 3: C. Tang: Appl. Phys. Lett., 48, 183 (1986)